[LinuxPPS] Using LinuxPPS for Event Counting

[Thiago Tiedtke]

Thanks all for the answers...

Realy, in some tests, i notice that the CPU load affect the dispatch time of
interrupts...but the LinuxPPS yet is a god choice im my experiments....with
more time, i go engage more time i'm tests with RTAI (Real Time Linux
Application)...

Yesterday, in a experiment, i try to use the ppsldisc in the follow
configuration:

 - MB Via Epia 600MHz itx, 512 Mb RAM, two serial ports;
- Debian Etch (kernel 2.6.27-rc3)   LinuxPPS (ntp-pps-2.6.27-rc3-bis.diff);
- GPS Novatel L1/L2 with PPS output: 1sec  /- 20ns;

Serial Port 1 (/dev/ttyS0):

- Receive the NMEA sentences and the pulse PPS from GPS (pin DCD);
- NTP with driver 20 (nmea.patch)
- After 15 minutes the estimated error is < 1 milisec

After the stabilization of clock, i'm activate ppsldic in the serial port 2
(/dev/ttyS1), whit the intention to use with other interrup source:

/usr/local/bin/ppsldisc /dev/ttyS1 &

But, checking the status of synchronization with ntpq -p, the signal PPS is
not more detected, and aparently the serial port /dev/ttyS0 stopped...no
more nmea setences, neither signal PPS...  :(

What is Wrong?? What is my mistake??

Thanks for any tips

Thiago Tiedtke dos Reis


2008/9/30 Rodolfo Giometti <giometti at enneenne.com>

>
> On Mon, Sep 29, 2008 at 10:57:17PM -0300, Thiago Tiedtke wrote:
>
> >    I'm using the LinuxPPS with ntp to adjust a pc clock, using the DCD
> pin to
> >    catch the PPS signal from gps, and NMEA messages from a GPS Novatel
> DL4
> >    ...and this is task is ok, my question is:
> >
> >    I can use the LinuxPPS to "poll" other type of events, e.g., a
> >    interruptor, or a photodiode ??
>
> Yes.
>
> >    By fact, i'm doing these tests, "catching" events with 1/1000s of
> >    duration...but without the regularity from signal PPS (e.g. at each 1
> sec
> >    +/- 20ns) from a GPS device....
> >
> >    This can be applied? What the "quality" of timestamp of each event?
>
> Mmm... the "quality" is the one that a non real-time kernel can
> do. LinuxPPS has been designed for current time estimation and the
> time stamp recording has been optimized to accomplish this task, but I
> don't know if this optiomization is enought for you. :) You should do
> some measurements by yourself to answer the question. Surely you can
> use it to record whatever-you-want's timestamps.
>
> Ciao,
>
> Rodolfo
>
> --
>
> GNU/Linux Solutions                  e-mail: giometti at enneenne.com
> Linux Device Driver                          giometti at linux.it
> Embedded Systems                     phone:  +39 349 2432127
> UNIX programming                     skype:  rodolfo.giometti
>
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